Static Factory Method instead of Constructors

• Names improve readability
• Different methods for different use cases
  • Only one constructor with same signature
• Caching possible
• Can return subtype
• Java8 allows static methods
• Allow service provider frameworks
  • e.g. JDBC, DriverManager.getConnection
• Also great for test fixtures
  • of(), from()...

Builder for many Constructor Parameters

• Static factories and constructors don't scale for large number of optional parameters
• Telescoping constructor as an anti pattern
  • Devs might confuse parameters with same type (compiler doesn't care(
• JavaBeans pattern
  • Empty contructor + setters
  • Creates partially inconsistent objects during creation
• Builder pattern instead
  • Create builder, set values (fluent), call build()
  • E.g. as static member class

Builder for Class Hierarchies

• Implement using a generic type with a recursive type paramter
• Builder<T extends Builder<T>>
• Use parent builder type in subclasses
• Beware: Problematic for other JVM languages (Kotlin, Scale)
• See Testcontainers GenericContianer

Builder for Class Hierarchies

• Implement using a generic type with a recursive type paramter
  
• Builder<T extends Builder<T>>
  
• Use parent builder type in subclasses
• Beware: Problematic for other JVM languages (Kotlin, Scale)
  
• See Testcontainers GenericContianer

Singleton

• Public static field
  • Easy to implement, but strong coupling
• Static factory method
  • Singleton becomes implementation detail
  • Use factory or runtime checking for testability?
• Single-element enum
  • Simple to implement
  • Strong guarantees

Can find improve the existing codebase? Examples?